The studies on maintenance of spermatogenesis in hypophysectomized rats with C21 steroids will be continued since data obtained so far do not provide clear evidence that the low rate of conversion of these steroids to androgens is sufficient to maintain spermatogenesis. The effect of estradiol on androgen production in the testes will be tested in hypophysectomized animals receiving LH replecement therapy. The effect of FSH in LH-simulated androgen production by the testes will be investigated in immature animals. We demonstrated in the past that LH treatment during development (from birth until 20 days of age) does not prevent the decrease of androgen production noted normally during this period of development. FSH modifies this response. Studies will be conducted utilizing an appropriate design (dose combination, time) to investigate this relationship utilizing as the end points both in vitro capacity of testicular tissue to convert appropriate radiolabeled precursors and cold mass of androgens. Study on formation of different molecular size of immunoprecipitable gonadotropins in incubates of pituitary tissue will be continued with species of gonadotropins from the viewpoint of their ability to induce biological response. BIBLIOGRAPHIC REFERENCES: Steinberger, E. and A. Steinberger. The spermatogenic function of the testis. In : Handbook of Physiology, Endocrinology V, Astwood, E and R. Greep (eds), Bethesda, Md. American Physiology Society, 1975, p. 1-19. Steinberger, E., A.K. Chowdhury, R. K. Tcholakian, and H. Roll. Effect of C21 steroids on sex accessory organs and testes of mature hypophysectomized rats. Endocrinology 96: 1319-1323, 1975.